This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The budding yeast kinetochore connects spindle microtubules to centromeric DNA and is critical in mitotic spindle function. A number of kinetochore proteins are phosphorylated by mitotic kinases but what impact these modifications have on their regulation has yet to be understood. Here we use mass spectrometry to map sites of phosphorylation, as well as in vivo studies, in order to understand the functional consequences of mutating these sites. This will allow us to gain more insight into the impact of phosphorylation on kinetochore protein interactions and the regulation of the mitotic spindle and budding yeast kinetochore.